Writing instrument



FIG. 1 is a front and right side perspective view of a writing instrument showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a left side view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a top view thereof; and,

FIG. 6 is a bottom view thereof. 

The ornamental design for a writing instrument, as shown and described. 